首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   622909篇
  免费   10728篇
  国内免费   1886篇
电工技术   10415篇
综合类   2842篇
化学工业   93541篇
金属工艺   24752篇
机械仪表   18596篇
建筑科学   15391篇
矿业工程   2841篇
能源动力   16111篇
轻工业   54184篇
水利工程   6594篇
石油天然气   9753篇
武器工业   39篇
无线电   69486篇
一般工业技术   119748篇
冶金工业   110041篇
原子能技术   10869篇
自动化技术   70320篇
  2022年   3492篇
  2021年   5573篇
  2020年   4079篇
  2019年   5138篇
  2018年   22119篇
  2017年   20932篇
  2016年   18210篇
  2015年   6933篇
  2014年   10384篇
  2013年   26190篇
  2012年   18885篇
  2011年   30095篇
  2010年   24401篇
  2009年   23734篇
  2008年   25210篇
  2007年   25709篇
  2006年   16204篇
  2005年   15807篇
  2004年   15073篇
  2003年   14906篇
  2002年   13485篇
  2001年   13120篇
  2000年   12215篇
  1999年   12835篇
  1998年   34168篇
  1997年   23775篇
  1996年   18024篇
  1995年   13353篇
  1994年   11567篇
  1993年   11239篇
  1992年   8001篇
  1991年   7499篇
  1990年   7319篇
  1989年   7073篇
  1988年   6546篇
  1987年   5815篇
  1986年   5702篇
  1985年   6332篇
  1984年   5957篇
  1983年   5209篇
  1982年   4945篇
  1981年   5030篇
  1980年   4760篇
  1979年   4654篇
  1978年   4446篇
  1977年   5437篇
  1976年   7164篇
  1975年   3833篇
  1974年   3578篇
  1973年   3714篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Ferroptosis is gaining followers as mechanism of selective killing cancer cells in a non-apoptotic manner, and novel nanosystems capable of inducing this iron-dependent death are being increasingly developed. Among them, polydopamine nanoparticles (PDA NPs) are arousing interest, since they have great capability of chelating iron. In this work, PDA NPs were loaded with Fe3+ at different pH values to assess the importance that the pH may have in determining their therapeutic activity and selectivity. In addition, doxorubicin was also loaded to the nanoparticles to achieve a synergist effect. The in vitro assays that were performed with the BT474 and HS5 cell lines showed that, when Fe3+ was adsorbed in PDA NPs at pH values close to which Fe(OH)3 begins to be formed, these nanoparticles had greater antitumor activity and selectivity despite having chelated a smaller amount of Fe3+. Otherwise, it was demonstrated that Fe3+ could be released in the late endo/lysosomes thanks to their acidic pH and their Ca2+ content, and that when Fe3+ was co-transported with doxorubicin, the therapeutic activity of PDA NPs was enhanced. Thus, reported PDA NPs loaded with both Fe3+ and doxorubicin may constitute a good approach to target breast tumors.  相似文献   
42.
Marrone  Mauricio  Lemke  Sascha  Kolbe  Lutz M. 《Scientometrics》2022,127(7):3857-3878
Scientometrics - Computer-assisted methods and tools can help researchers automate the coding process of literature reviews and accelerate the literature review process. However, existing...  相似文献   
43.

Probabilistic topic modeling algorithms like Latent Dirichlet Allocation (LDA) have become powerful tools for the analysis of large collections of documents (such as papers, projects, or funding applications) in science, technology an innovation (STI) policy design and monitoring. However, selecting an appropriate and stable topic model for a specific application (by adjusting the hyperparameters of the algorithm) is not a trivial problem. Common validation metrics like coherence or perplexity, which are focused on the quality of topics, are not a good fit in applications where the quality of the document similarity relations inferred from the topic model is especially relevant. Relying on graph analysis techniques, the aim of our work is to state a new methodology for the selection of hyperparameters which is specifically oriented to optimize the similarity metrics emanating from the topic model. In order to do this, we propose two graph metrics: the first measures the variability of the similarity graphs that result from different runs of the algorithm for a fixed value of the hyperparameters, while the second metric measures the alignment between the graph derived from the LDA model and another obtained using metadata available for the corresponding corpus. Through experiments on various corpora related to STI, it is shown that the proposed metrics provide relevant indicators to select the number of topics and build persistent topic models that are consistent with the metadata. Their use, which can be extended to other topic models beyond LDA, could facilitate the systematic adoption of this kind of techniques in STI policy analysis and design.

  相似文献   
44.
Journal of Materials Science: Materials in Electronics - Nano Mn0.95M0.05S (M ≡ Cu, Mg) samples were produced using molten salt solid state reaction method. Rietveld analysis of X-ray...  相似文献   
45.
Journal of Engineering Physics and Thermophysics - Results of investigation into the influence of a corrosion process on thermotechnical characteristics of heat pipes of low-temperature range are...  相似文献   
46.
Deshmukh  P.  Sar  S. K.  Smječanin  N.  Nuhanović  M.  Lalwani  R. 《Radiochemistry》2022,64(4):532-542
Radiochemistry - Magnetically modified waste bark of the Aegle marmelos tree was prepared by using green synthesis method and was used in a batch system for U(VI) removal from aqueous solution. The...  相似文献   
47.
Kamar  M. S.  Shalan  A. S.  Youssef  W. M.  Hussein  A. E. M.  Khawassek  Y. M.  Taha  M. H. 《Radiochemistry》2022,64(2):244-256
Radiochemistry - Ferrugination, sericitization, desulfitization, chloritization, and kaolinitization of hydrothermal origin are the main wall rock alterations occurring within the NNW shear zones...  相似文献   
48.
Bioactive glasses and glass-ceramics (GCs) effectively regenerate bone tissue, however most GCs show improved mechanical properties. In this work, we developed and tested a rarely studied bioactive glass composition (24.4K2O-26.9CaO-46.1SiO2-2.6P2O5 mol%, identified as 45S5-K) with different particle sizes and heating rates to obtain a sintered GC that combines good fracture strength, low elastic modulus, and bioactivity. We analyzed the influence of the sintering processing conditions in the elastic modulus, Vickers microhardness, density, and crystal phase formation in the GC. The best GC shows improved properties compared with its parent glass. This glass achieves a good densification degree with a two-step viscous flow sintering approach and the resulting GC shows as high bioactivity as that of the standard 45S5 Bioglass®. Furthermore, the GC elastic modulus (56 GPa) is relatively low, minimizing stress shielding. Therefore, we unveiled the glass sintering behavior with concurrent crystallization of this complex bioactive glass composition and developed a potential GC for bone regeneration.  相似文献   
49.
50.
Russian Engineering Research - The modernization of manufacturing by the comprehensive application of digital technology—in both production and management—is considered. Principles are...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号